Flop Fix

INSTRUCTIONS

Information for the program FLOP_FIX.PRG
****************************************

FLOP_FIX.PRG is an error correction program for the unfortuantely all too
common problem with the BIOS diskette routines in TOS versions 2.06, 3.06,
4.01, 4.02 and 4.04.

!!! This error still exists in TOS4.00 but since I do not have this version
you should take this into consideration!!! A TOS4.03 probably doesn't exist.

FLOP_FIX.PRG is freeware. It may be copied and distributed freely by anyone 
provided this text is included. It may be placed in mail boxes and 
translations to other languages is particularly desired.

The author has carefully checked the program for accuracy but can bear no 
resposibility for any loss of data or damage caused bu the usage of this 
program or this information file. The user carries the reponsibility for 
the use (or non-use) of this patch program themselves.

Please read through this file to the end otherwise you may possibly miss 
something.


Operation
*********

FLOP_FIX.PRG should be placed in your AUTO folder (possibly as the first 
program). It will install itself only when it has been able to identify a 
TOS version as previously described in these instructions and then takes a 
little over 1Kbyte of memory.  It work equally well whether TOS risides in 
ROM or has been relocated in RAM. A message will appear in the event of its 
installation (or non-installation). FLOP_FIX must be run before any other 
programs that intercept the XBIOS vector (trap#14). Otherwise the only 
result will be an appropriate message. All messages are provided in English 
but are generally understandable. FLOP_FIX can also be started from the 
desktop. A multiple installation will not cause any problems except for a 
loss of a little over 1 Kbyte of memory.

I should now make clear that to ensure that the operating system works 
faultlessly, at least one AUTO folder program and at least one accessory 
should have their fastload bits unset. Usefully, the first program may not 
have this set which is the case with FLOP_FIX.PRG. If it has indeed been 
set, the following ones may have problems (with TOS 1.04, bombs may 
result).

Interna
*******

FLOP_FIX appends itself to the hdv_bpb and the hdv_rw vectors using the 
XBRA identifier T206 and replaces the TOS floppy Getbpb routine completely 
and the rwabs routine partially. Even though during installation, it is 
necessary for FLOP_FIX to test the XBIOS vector, it does not change it.


The (removal of) four errors
****************************
TOS2.06/3.06/4.0x calculates a checksum from the first six sectors of a 
diskette, which it uses to make sure a disk change is recognized. 
Unfortunately, it is unable to differentiate between drive A and Drive B. 
Thus this error will only be observed when you have a drive B e.g. if you 
have a long text file on a write-protected diskette in drive B that you wish
to display from the desktop, when adressed for the second time to load the 
next portion of the text you will receive a message -READ ERROR-  (in this 
case a disk change has been identified when none has taken place).

In principle, TOS2.06/3.06/4.0x can only process media with one FAT (in 
which case GEMDOS works correctly). To do this, bit 1 of the flag (offset 
$10) in the Bios Parameter Block must be set to 1. The floppy Getbpb 
routine does indeed set this bit but wrongly determines the sector layout 
of the diskette. Thus this error will only be identified when you are using 
disks that have been formatted with only one FAT. Normally disks have two 
FATs.

Additionally, the Rwabs routine is still missing an abort operation when re-
calculating the sector checksum for sectors 0 to 5. When you use rwabs to 
write more than one sector that starts between 0 and 5, then possibly VDI
information regarding the text style, size and font can be overwritten. The 
result is a very strange looking desktop. Basically the first of these 
errors will only occur when using diksteets with more than 13 sectors per 
track. Gemdos itself removes this error but probably never does


History
*******

A program of mine PATCHX06.PRG does exist that is only suitable for TOS2.06 
and TOS3.06. FLOP_FIX does not include any functional changes, it is only 
expanded for use with TOS4.0x.


ED diskettes
************

FLOP_FIX.PRG also enables the correct processing of ED diskettes (2.88 
mbyte) with either a 12-bit FAT (these disks use at least 2 sectors per 
cluster) or a 16-bit FAT (these disks have 1 sector per cluster). The 
difference in the FAT sizes is a result of an analogy to MSDOS in regard to 
the number of data clusters. Up to, and inclusive of 4078 data clusters can 
be accomodated by a 12-bit FAT. With more that 4079 data clusters, a 16-bit 
FAT is used. Calculation tip: The changover does not in fact result from 
>4096 clusters, since some of the clusters are reserved for internal use 
($FF0-$FFF) plus ($000, $001).


The author
**********

I am a student and use the computer for my studies. I hope that I will not 
have to continue develop this program in the future, since Atari has 
removed this error in the un-official Beta test TOS4.92.

I am only providing my address. If you really require my telephone number, 
you will find it in the telephone directory. If anyone contacts me outside 
of the hours 07.00 and 21.00 (Central European Time or Central European 
Summer Time) they will make themselves extremely unpopular! I would like at 
this point to thank all those invoved in the development of this patch.

Berlin, 28.08.1992


Harun Scheutzow
Dresdener Straže 83
D-10179 Berlin

or via EMail
in the Mausnetz: Harun Scheutzow @B
or the Internet: Harun_Scheutzow@B.maus.de